#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int f_num(int n)
{
	int a = 1;
	int b = 1;
	int c = 0;
	while (n >= 3)
	{
		c = a + b;
		a = b;
		b = c;
		n--;
	}
	return c;
}
int main()
{
	int i = 0;
	scanf("%d", &i);

	int ret = f_num(i);

	printf("%d", ret);


	return 0;
}












